Update! Click here (Essential Tips for Cropping in Photoshop CC) to see all tips for working with color in Photoshop CC in a single post.
When compositing several images in a single document I often find that a portion of a layer (or portions of multiple layers) will end up being positioned outside of the visible image area. Photoshop, of course, is still keeping track of this information (in case I choose to reposition the layer), but when I’m certain that I will no longer need it, I can choose Select > All and then Image > Crop. This eliminates unnecessary information outside or beyond the visible image area and will typically help to keep my file size more manageable.
Note: when working with Smart Objects, Photoshop will still keep the additional information, regardless of whether or not you crop the document.